Turkish police have arrested an Iranian lawyer who represented Sakineh Mohammadi Ashtiani, the woman sentenced to death by stoning for adultery.

Mohammad Mostafaei went into hiding after Iranian authorities detained three of his relatives and issued a warrant for his arrest. Mostafaei's brother-in-law and father-in law were subsequently released, but his wife remains in solitary confinement in Evin prison, although she has not been charged with any offence.

Mostafaei was apparently smuggled into Turkey but was arrested on immigration charges on Monday.

Human rights activists expressed concern for Mostafaei's safety and the possibility that Turkey, an ally of Iran, might return him. "He was treated very poorly by the Turkish police and was threatened that they might send him back to Iran," said Shadi Sadr, an Iranian human rights activist who spoke with Mostafaei by phone today. Mostafaei was concerned about his seven-year-old daughter who is with his wife's family in Iran.

The Guardian understands Norwegian and US officials met Mostafaei in prison and offered him asylum, but he was forced by Turkish officials to claim asylum with the UNHCR in Turkey or face extradition.

Amnesty International also expressed concern for his safety. Drewery Dyke of Amnesty's Iran team said: "We call upon the authorities to expedite Mostafaei's asylum request as he had a death threat in Turkey and is a target of the Iranian officials because of his involvement with Mohammadi Ashtiani's case."

"The Turkish government is in close co-operation with other authorities to grant him asylum as soon as possible," said Orhan Tung, a Turkish embassy spokesman in London. The embassy said the foreign ministry would not comment on concerns over Mostafaei's safety. Mohammadi Ashtiani's son Sajad had expressed hope that Turkey would join Brazil in raising the issue with Iran.

Iranian authorites today told Mohammadi Ashtiani's current lawyer, Houtan Kian, that she still faces death by hanging. A final decision would be made next week.